The intrinsic properties of neurons can be modified by changes in their electrical activity. Though much less studied than synaptic plasticity, activity-dependent modifications of intrinsic neuronal properties can have an important impact on neural network function. The proposed research is part of an ongoing study of how oscillatory and plateau properties of individual neurons affect network behavior. In previous work, neuron models with dynamically regulated conductances were constructed and shown to display interesting activity-dependent changes when perturbed, stimulated or coupled into networks. Related experimental work showed that the intrinsic properties of stomatogastric ganglion (STG) neurons in primary cell culture are dramatically modified by prolonged shifts in their patterns of activity. The STG also modifies its mode of operation, both in organ culture and in vivo, when changes in its modulatory inputs suppress activity. As part of a continuing analysis of the dynamics of oscillatory networks, these phenomena will be studied and modeled in detail. Specifically the proposed research will: l) Study the effects of activity on the intrinsic properties of single STG neurons in primary cell culture and model the dynamics of the conductance changes seen. 2) Construct two- and three-cell networks of cultured STG neurons using both artificial and naturally occurring synapses to study the impact of intrinsic plasticity on network function. Parallel modeling studies will explore this question and study the interplay between intrinsic and synaptic plasticity. 3) Study the plasticity of the full pyloric circuit of the STG in organ culture and in vivo. Dynamic regulation of conductances will be used as a tool to construct a model of the pyloric network and then to explore its development and study how perturbations in its modulatory environment induce long-term changes in its properties.